1. Field of the Invention
The present invention relates to a light irradiation method and a light irradiation system for increasing or decreasing a perceived brightness of a target, which is illuminated, by performing time-wise control of prescribed illumination light.
2. Description of the Related Art
Various illumination methods for increasing a brightness perceived regarding an illuminated target (hereinafter, referred to as, for example, a "perceived brightness of a target") have been studied. From a practical point of view, the entirety of the inside of a room is set as a target, and researches on methods for increasing the perceived brightness of a target are performed.
According to one of the methods developed so far, walls of the room are illuminated to be brighter than the rest of the room, instead of uniformly illuminating the entirety of the inside of the room. Thus, the entirety of the inside of the room is perceived to be brighter at an equal energy consumption. According to another method developed so far, a painting on the wall or a table in the room is spot-illuminated. Thus, the inside of the room is perceived to be brighter. Furthermore, according to the method recently proposed in Japanese Laid-Open Publication No. 8-279306, a "sparkling" light emitting section which is small in size but has a high luminance is included in an illumination device, so that the inside of the room is perceived to be brighter.
Regarding a target located indoors, for example, K. Hashimoto et al., "Visual Clarity and Feeling of Contrast", Color Res. Appl., Vol. 19-3, pp. 171-185 (1994) and K. Hashimbto et al., "Method for evaluating the color rendering property of a light source based on the consciousness", the Journal of the Illuminating Engineering Institute of Japan, Vol. 79, No. 11, pp. 29-37 (1995) describe that a perceived brightness of an indoor target can be raised by utilizing the phenomenon that the colorfulness of a target is increased when illuminated with a lamp having a superior color rendering property.
In a recent study performed by Ikeda et al., information obtained from various objects seen by an observer when he/she enters the room is referred to as "initial visual information", and illumination states of the inside of the room recognized based on the initial visual information including the brightness of the room is referred to as"illumination recognition visual space". Ikeda et al. has studied physical factors which determine the initial visual information and the illumination recognition visual space. As a result, it is reported that when two rooms which are different only in the brightness (reflectance) of the walls are located side by side and illuminated under the same conditions, the tone of gray color is perceived to be brighter in the room having a brighter wall (having a wall of a higher reflectance) than in the other room (Mizogami et al., "Apparent brightness based on the concept of the illumination recognition visual space", the Proceedings of the 31st (1998) Annual Conference of the Illuminating Engineering Institute of Japan, 136, page 227 (1998)).
The above-mentioned studies indicate that a perceived brightness of the target can be increased under various conditions without increasing the amount of light directly illuminating the target.
However, the above-mentioned conventional methods are all for increasing a perceived brightness of a target. Conventionally, no method for effectively decreasing a perceived brightness of a target by performing time-wise control of light intensity without changing the amount of light directly illuminating the target has been utilized. For this reason, the conventional art has not succeeded in effectively changing (increasing and decreasing) a perceived brightness of a target.